1. Field of the Invention
This invention relates to a protective housing for accommodating a scale member and a longitudinally movable scanning unit of a length measuring system, which comprises a housing tube, which is adapted to support the scale member and preferably has a basically rectangular cross-section and one narrow side wall is formed with a slot, which is adapted to receive an actuating member, which is adapted to be coupled to the scanning unit, and which housing tube is adapted to be closed at both ends by end closures, which are adapted to hold said housing in position and protrude beyond the ends of the housing tube.
2. Description of the Prior Art
The protective housing is intended for use in length measuring systems consisting of absolute length measuring systems or of incremental length measuring systems. In both cases the scanning unit is movable along the scale member by means of the actuating member and is adapted to scan the scale member or a measuring scale provided on the scale member, which is adapted to be scanned by said scanning unit by optoelectronic, capacitive or inductive scanning methods and to generate measured-value signals or to read the scale member as a result of such scanning. The interior of the housing tube must be protected from being soiled. Besides, it is desired to ensure that the scale member will be in the correct measuring position when the housing is mounted by means of the end closures. It is known that the end closures may consist of shaped bodies, which are mounted at the ends of the housing tube, which at said ends has inside surfaces which are complementary to extensions of the shaped bodies. Such an arrangement has the disadvantage that an expensive machining of the end closures and of the tube end portions is required, that an absolutely exact alignment of the end closures is not achieved in many cases and that the necessary sealing of the tube at its ends is not achieved in many cases.